WO2024255217A1 - Modified chitosan and preparation method therefor, and retardation-type water-reducing agent and use thereof - Google Patents

Abstract

The present invention belongs to the technical field of building materials. Disclosed are a modified chitosan and a preparation method therefor, and a retardation-type water-reducing agent and the use thereof. The modified chitosan provided in the present invention is a compound in which a chitosan molecular chain is bonded with an amino acid-like chelating structure, wherein the amino acid-like chelating type structure can play a synergistic role with a steric effect of a spatial three-dimensional structure of the chitosan itself. The addition of the modified chitosan can make the concentration of metal ions in an early concrete slurry be in a dynamic equilibrium state, thereby achieving an effect of reducing the early hydration rate. In addition, a certain amount of hydroxyl is further reserved on the molecular chain of the modified chitosan, such that a large amount of water can be adsorbed while metal ions are chelated, thereby promoting a later hydration reaction of the concrete. The water-reducing agent obtained by compounding the modified chitosan provided in the present invention with other components, such as polycarboxylic acid, has good water reducing performance, retarding performance and slump retaining performance, and has good application prospects.

Description

A modified chitosan and its preparation method, slow-setting water reducing agent and application

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of the Chinese patent application with application number 202311736218.9 filed with the Chinese Patent Office on December 18, 2023, entitled "A modified chitosan, its preparation method, slow-setting water reducer and application", the entire contents of which are incorporated by reference in this application.

Technical Field

The invention belongs to the technical field of building materials, and in particular relates to a modified chitosan and a preparation method thereof, a slow-setting water reducing agent and application thereof.

Background Art

As a commonly used chemical admixture in existing concrete, polycarboxylate water-reducing agent is widely used due to its advantages of low dosage, high water reduction, designable molecular structure, and green environmental protection. However, the interaction between polycarboxylate water-reducing agent and concrete will affect the flow properties of cement paste and cause abnormal coagulation of cement paste. At present, by adding retarding substances such as chitosan and polyether to polycarboxylate water-reducing agent, the problem of deterioration of concrete paste flow properties caused by the addition of polycarboxylate water-reducing agent is expected to be improved.

However, in actual use, the addition of chitosan, polyether and other substances can alleviate the impact of polycarboxylic acid water reducer on concrete paste to a certain extent, but the above substances also often have compatibility problems with cement, machine-made sand, and mineral admixtures (fly ash, mineral powder, etc.) in concrete, which in turn has an adverse effect on the performance of concrete (such as hydration and coagulation, curing performance, strength, hardness and other mechanical properties), or affects the water-reducing effect of polycarboxylic acid, which greatly restricts the application of polycarboxylic acid water reducer. Therefore, it is necessary to develop more adaptable retarding substances to meet actual needs.

Summary of the invention

The first purpose of the present invention is to solve the adverse effects of adding a retarder in the prior art on the water-reducing effect of polycarboxylic acid and the performance of concrete, thereby obtaining a modified chitosan having excellent water-reducing performance, retarding performance and collapse-retaining performance.

The second object of the present invention is to provide a method for preparing modified chitosan.

The third object of the present invention is to provide modified chitosan prepared by the above method.

A fourth object of the present invention is to provide a slow-setting water-reducing agent.

The fifth object of the present invention is to provide application of modified chitosan and/or slow-setting water reducing agent in the field of construction.

Specifically, the modified chitosan is a compound having an amino acid chelate-like structure bonded to the chitosan molecular chain, and the structure of the modified chitosan includes at least one of the structural unit 1 represented by formula (1), the structural unit 2 represented by formula (2), and the structural unit 3 represented by formula (3);

In formulas (1) to (3), _R1 , _R2 , _R3 , _R4 , _R5 and _R6 are independently carbonyl, C1-C4 alkylene, C1-C4 haloalkylene, C1-C4 carboxylic acid group, C1-C4 halocarboxylic acid group, C1-C4 acylene or C1-C4 haloacylene. In some specific embodiments, in formulas ( ₁ ) to (3), _R1 , _R2 , _R3 , _{R4 , R5} and _R6 are independently _{-CH2CO-, -CH2CH2CO- ,} -CH2CH2CH2CO-, _-CH2CH2- , -CH[ _CH2 ( _Cl )COOH]- or -CH[ _CH2 (Br) _COOH ]-.

In some specific embodiments, the chitosan is oligo-chitosan and/or high-molecular-weight chitosan.

In some specific embodiments, the weight average molecular weight of the modified chitosan is 300 to 50,000, and the molecular weight distribution is 1.2 to 1.35.

The preparation method of the modified chitosan provided by the invention comprises: taking chitosan and halogenated carboxylic acid to carry out halogenated carboxylation reaction under the action of a catalyst to obtain the modified chitosan.

In some specific embodiments, the weight average molecular weight of the chitosan is 300-50,000.

In some specific embodiments, the halogenated carboxylic acid is selected from 3-chloropyruvic acid, 3-bromopyruvic acid, One or more of 2-dichlorosuccinic acid, 2,3-dichlorosuccinic acid, 3-chloropropionic acid and 3-bromopropionic acid.

In some specific embodiments, the catalyst is selected from one or more of a Ziegler-Natta catalyst, a MOFs catalyst and a copper oxide catalyst.

In some specific embodiments, the molar ratio of chitosan to halogenated carboxylic acid is (0.01-2):1.

In some specific embodiments, the catalyst is added in an amount of 0.01 to 0.5 wt % based on the total molar amount of the chitosan and the halogenated carboxylic acid.

In some specific embodiments, the temperature of the halogenated carboxylation reaction is 85-95° C. and the time is 4-10 hours.

The invention provides modified chitosan prepared by the above method.

The slow-setting water-reducing agent provided by the present invention comprises the above modified chitosan.

In some specific embodiments, the slow-setting water-reducing agent further comprises polycarboxylic acid, an air entraining agent and a water-retaining agent.

In some specific embodiments, the content of modified chitosan in the slow-setting water-reducing agent is 15-50 parts by mass, the content of polycarboxylic acid is 50-80 parts by mass, the content of air entraining agent is 0.1-0.5 parts by mass, and the content of water-retaining agent is 0.1-0.5 parts by mass.

The present invention also provides the application of the chitosan and/or slow-setting water reducing agent in the field of construction.

The present invention introduces a chelating structure similar to an amino acid into the basic molecular chain structure of chitosan, thereby obtaining a modified chitosan. The water reducing agent obtained by compounding the modified chitosan as a retarder with other components such as polycarboxylic acid has excellent water reducing performance, retarding performance and slump retention performance, and has good application prospects. It is speculated that the reason why the modified chitosan provided by the present invention has the above excellent properties is that the chelating structure similar to an amino acid introduced into the chitosan molecular chain structure can work synergistically with the steric effect of the spatial structure of chitosan itself, giving the modified chitosan a good ability to chelate with metal ions such as calcium, aluminum, and magnesium dissolved in the concrete slurry and a certain water-reducing and dispersing effect, so that the metal ion concentration in the early concrete slurry added with the modified chitosan can be in a dynamic equilibrium state, thereby reducing the early hydration rate; and because the modified chitosan also retains a certain amount of hydroxyl groups, the modified chitosan can absorb a large amount of water while chelating metal ions, thereby promoting the late hydration reaction of the concrete.

DETAILED DESCRIPTION

The modified chitosan provided by the present invention is a compound having an amino acid chelate-like structure bonded to the chitosan molecular chain, wherein the structure of the modified chitosan comprises at least one of the structural unit 1 represented by formula (1), the structural unit 2 represented by formula (2) and the structural unit 3 represented by formula (3);

In formulae (1) to (3), _R1 , _R2 , _R3 , _R4 , _R5 and _R6 are independently carbonyl, C1-C4 alkylene, C1-C4 halogenated alkylene, C1-C4 carboxylic acid group, C1-C4 halogenated carboxylic acid group, C1-C4 acylene or C1-C4 halogenated acylene. Examples of C1- _C4 alkylene include, but are not limited to, _-CH2- , _-CH2CH2- , _-CH ( _CH3 ) _{- , -CH2CH2CH2-} , -C( _{CH3 ) 2- or -CH2CH2CH2CH2-} . Examples of C1-C4 haloalkylene groups include, but are not limited to, -CH(Cl)-, -CH(Br) _CH2- , -C[Br( _CH3 )]- _, -CH( _Br ) _CH2CH2- , -C[ _CH2 (Cl) _CH3 ]-, or _-CH2CH2CH (Br) _CH2- . Examples of C1-C4 carboxylic acid groups include, but are not limited to, -CH(COOH)-, _-CH2CH (COOH)-, or -CH( _CH3 )CH(COOH)-. Examples of C2-C4 acyl groups include, but are not limited to, _{-CH2CO- , -CH2CH2CO- , -CH} ( _CH3 ) _CO- , _{-CH2CH2CH2CO-} , or -C( _CH3 ) _2CO- . Examples of C2-C4 haloacyl include, but are not limited to, -CH(Br)CO-, _-CH2CH (Cl)CO-, or -CH( _CH3 )CH(Br ₎ CO- _. In some preferred embodiments, _R1 , _R2 , _R3 , _R4 , _R5 , and _R6 are independently _{-CH2CO-, -CH2CH2CO- ,} -CH2CH2CH2CO- _, -CH2CH2-, -CH[ _CH2 (Cl)COOH]-, or -CH _{[ CH2} (Br) _COOH ]-.

The structure of the modified chitosan provided by the present invention may also include one or more of the structural unit 4 shown in formula (4), the structural unit 5 shown in formula (5), the structural unit 6 shown in formula (6) and the structural unit 7 shown in formula (7):

In formulae (5) to (7), R ₇ , R ₈ , R ₉ and R ₁₀ are independently carbonyl, C1-C4 alkylene, C1-C4 halogenated alkylene, C1-C4 carboxylic acid group, C1-C4 halogenated carboxylic acid group, C1-C4 acylene or C1-C4 halogenated acylene. Examples of C1-C4 alkylene include, but are not limited to, -CH ₂ -, -CH ₂ CH ₂ -, -CH(CH ₃ )-, -CH ₂ CH ₂ CH ₂ -, -C(CH ₃ ) ₂ - or -CH ₂ CH ₂ CH ₂ CH ₂ -. Examples of C1-C4 haloalkylene groups include, but are not limited to, -CH(Cl)-, -CH(Br) _CH2- , -C[Br( _CH3 )]- _, -CH( _Br ) _CH2CH2- , -C[ _CH2 (Cl) _CH3 ]-, or _-CH2CH2CH (Br) _CH2- . Examples of C1-C4 carboxylic acid groups include, but are not limited to, -CH(COOH)-, _-CH2CH (COOH)-, or -CH( _CH3 )CH(COOH)-. Examples of C2-C4 acyl groups include, but are not limited to, _{-CH2CO- , -CH2CH2CO- , -CH} ( _CH3 ) _CO- , _{-CH2CH2CH2CO-} , or -C( _CH3 ) _2CO- . Examples of C2-C4 haloacyl include, but are not limited to, -CH(Br)CO-, _-CH2CH (Cl)CO-, or -CH( _CH3 )CH(Br ₎ CO- _. In some preferred embodiments, _R1 , _R2 , _R3 , _R4 , _R5 , and _R6 are independently _{-CH2CO-, -CH2CH2CO- ,} -CH2CH2CH2CO- _, -CH2CH2-, -CH[ _CH2 (Cl)COOH]-, or -CH _{[ CH2} (Br) _COOH ]-.

In the present invention, “one”, “two”, “three”, “four”, “five”, “six” and “seven” in structural unit one, structural unit two, structural unit three, structural unit four, structural unit five, structural unit six and structural unit seven are merely for distinction to facilitate description and have no other special meaning.

In the present invention, the ratio of structural unit 1, structural unit 2, structural unit 3, structural unit 4, structural unit 5, structural unit 6 and structural unit 7 in the modified chitosan structure is not particularly limited, that is, the ratio of structural unit 1, structural unit 2, structural unit 3, structural unit 4, structural unit 5, structural unit 6 and structural unit 7 in the modified chitosan structure provided by the present invention can be The ratio of the present invention is 1:2:1:1:3:6:2, 2:5:9:3:1:1:1, 9:1:8:2:1:7, 100:5:135:1:4:3:6 or any other ratio; the distribution of the structural unit one, structural unit two, structural unit three, structural unit four, structural unit five, structural unit six and structural unit seven in the modified chitosan structure is not particularly limited, that is, the structural unit one, structural unit two, structural unit three, structural unit four, structural unit five, structural unit six and structural unit seven in the modified chitosan structure provided in the present invention can be distributed in any manner.

In the present invention, examples of the chitosan molecules include, but are not limited to, oligomeric chitosan and/or high molecular weight chitosan. In some specific embodiments, the polymerization degree of the oligomeric chitosan is preferably any integer in the range of 2 to 20, such as 2, 3, 5, 8, 10, 13, 15, 17, 20 or any integer therebetween. In some specific embodiments, the polymerization degree of the high molecular weight chitosan is exemplarily any integer in the range of 21 to 2000, such as 21, 30, 50, 100, 500, 1000, 1200, 1500, 2000 or any integer therebetween; the polymerization degree of the high molecular weight chitosan is preferably 21 to 200.

In the present invention, the weight average molecular weight of the modified chitosan is preferably 300 to 50000, such as 300, 500, 1000, 2000, 4000, 4210, 4300, 4520, 5000, 6000, 7500, 7801, 8000, 9000, 10000, 20000, 30000, 40000, 50000 or any value therebetween. The molecular weight distribution of the modified chitosan is preferably 1.2 to 1.35, such as 1.2, 1.21, 1.24, 1.27, 1.3, 1.33, 1.35 or any value therebetween.

The preparation method of the modified chitosan provided by the present invention comprises: taking chitosan and halogenated carboxylic acid to carry out halogenated carboxylation reaction under the action of a catalyst to obtain the modified chitosan

In the preparation of the modified chitosan, the weight average molecular weight of the chitosan is preferably 300-50000, such as 300, 500, 1000, 2000, 1000, 2000, 3000, 7500, 10000, 10200, 14600, 20000, 30000, 40000, 50000 or any value therebetween.

In the preparation process of the modified chitosan, the halogenated carboxylic acid is a compound containing both a halogen atom and a carboxylic acid in the molecule, which can undergo a halogenated carboxylic acid reaction with chitosan, and the halogenated carboxylic acid can be directly purchased or prepared by conventional methods. In some preferred embodiments, specific examples of the halogenated carboxylic acid include, but are not limited to, one or more of 3-chloropyruvic acid, 3-bromopyruvic acid, 2-dichlorosuccinic acid, 2,3-dichlorosuccinic acid, 3-chloropropionic acid, and 3-bromopropionic acid.

In the preparation process of the modified chitosan, the halogenated carboxylic acid reaction is defined as: under the action of a catalyst, the halogenated carboxylic acid removes the halogen atom to form a carbon positive intermediate, and the carbon positive intermediate attacks the amino group on the chitosan to form a carbon-nitrogen bond and removes hydrogen ions to obtain a modified chitosan having at least an amino acid chelate-like structure.

In the preparation process of the modified chitosan, the catalyst is a compound that can at least catalyze the halogenated carboxylic acid and the amino group on the chitosan molecular chain to undergo a halogenated carboxylic acid reaction, which can be directly purchased or prepared by conventional methods. In some preferred embodiments, specific examples of the catalyst include, but are not limited to, one or more of a Ziegler-Natta catalyst, a MOFs catalyst, and a copper oxide catalyst.

In the preparation process of the modified chitosan, the molar ratio of chitosan to halogenated carboxylic acid is preferably (0.01-2):1, such as 0.01:1, 0.05:1, 0.1:1, 0.18:1, 0.21:1, 0.5:1, 0.9:1, 1.02:1, 1.5:1, 2:1 or any value therebetween.

In the preparation process of the modified chitosan, based on the total molar amount of chitosan and halogenated carboxylic acid, the added amount of the catalyst is preferably 0.01-0.5wt%, such as 0.01wt%, 0.05wt%, 0.1wt%, 0.2wt%, 0.35wt%, 0.4wt%, 0.5wt% or any value therebetween.

In the preparation process of the above-mentioned modified chitosan, the conditions of the halogenated carboxylation reaction include a temperature of preferably 85 to 95°C, such as 85°C, 87°C, 88°C, 90°C, 91°C, 92°C, 94°C, 95°C or any value therebetween; and a time of preferably 4 to 10 h, such as 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h or any value therebetween.

The present invention also provides a modified chitosan prepared by the above method, wherein the structure of the modified chitosan has at least one of the structural unit 1 represented by formula (1), the structural unit 2 represented by formula (2) and the structural unit 3 represented by formula (3); in addition, the modified chitosan may also have one or more of the structural unit 4 represented by formula (4), the structural unit 5 represented by formula (5), the structural unit 6 represented by formula (6) and the structural unit 7 represented by formula (7).

The slow-setting water-reducing agent provided by the present invention includes the modified chitosan described above. In some preferred embodiments, the slow-setting water-reducing agent preferably also includes polycarboxylic acid, air entraining agent and water-retaining agent. Among them, the polycarboxylic acid is a reagent commonly used in existing water-reducing agents; it can be directly purchased or prepared by existing conventional methods. Specific examples of the air entraining agent can be, but are not limited to: a surfactant with low surface tension, the addition of which can enable the concrete to produce a large amount of uniform The air-entraining agent can be directly purchased or prepared by conventional methods. The specific example of the water-retaining agent can be, but is not limited to, a highly absorbent resin, which can improve the compressive strength, impermeability and durability of concrete by adding it; the water-retaining agent can be directly purchased or prepared by conventional methods.

In the present invention, the slow-setting water-reducing agent contains modified chitosan, and preferably also contains polycarboxylic acid, air entraining agent and water-retaining agent. Among them, the content of the modified chitosan is preferably 15 to 50 parts by mass, such as 15, 20, 25, 30, 35, 40, 45, 50 parts by mass or any value therebetween. The content of the polycarboxylic acid is preferably 50 to 80 parts by mass, such as 50, 55, 60, 65, 70, 75, 80 parts by mass or any value therebetween. The content of the air entraining agent is preferably 0.1 to 0.5 parts by mass, such as 0.1, 0.2, 0.3, 0.4, 0.5 parts by mass or any value therebetween. The content of the water-retaining agent is preferably 0.1 to 0.5 parts by mass, such as 0.1, 0.2, 0.3, 0.4, 0.5 parts by mass or any value therebetween.

In addition, the present invention also provides the application of the modified chitosan and/or slow-setting water reducing agent in the field of construction.

Embodiments of the present invention are described in detail below, and the examples of the embodiments are intended to be used to explain the present invention, but should not be construed as limiting the present invention. In the embodiments, if specific techniques or conditions are not specified, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not specified for reagents or instruments used, they are all conventional products that can be obtained commercially.

The raw materials and sources used in the following examples are as follows:

Air entraining agent (manufacturer is Nanjing Xinyi Synthetic, product number is XY-A01); water retention agent (manufacturer is Ningbo Zhongshuike, product number is SK-530); polycarboxylic acid (manufacturer is Kezhijie, product number is Point-400S); PCE-S (manufacturer is Kezhijie, product number is Point-MS); Sika retarder H-1 (manufacturer is Sika, product number is POWDER P).

Preparation Example 1

This preparation example is used for the modified chitosan and the preparation method thereof provided by the present invention. The preparation of the modified chitosan is specifically as follows: 3-bromopyruvic acid and chitosan (weight average molecular weight is 2000) are dissolved in butyl acetate according to a molar ratio of 1:0.1, and 0.05wt% of Ziegler-Natta catalyst is added, and stirred at 90°C for reaction. After 6 hours, the mixture was filtered, washed and dried to obtain modified chitosan.

After testing, the infrared spectrum of the modified chitosan obtained showed a CN absorption peak of secondary amine near 1270 cm ^-1 ; a C=O absorption peak of carboxylate appeared near 1600 cm ^-1 , and an absorption peak of ketone group appeared near 1715 cm ^-1 . It can be seen that an amino acid chelate structure is indeed introduced into the structure of the modified chitosan obtained, and the weight average molecular weight of the modified chitosan obtained is 4725, and the molecular weight distribution is 1.32.

Preparation Example 2

This preparation example is used for the modified chitosan and preparation method thereof provided by the present invention. The preparation of the modified chitosan is specifically as follows: 3-bromopyruvic acid and chitosan (weight average molecular weight is 5000) are dissolved in butyl acetate according to a molar ratio of 1:1, and 0.15wt% of Ziegler-Natta catalyst is added. After stirring and reacting at 90°C for 6h, the reaction is filtered, washed and dried to obtain the modified chitosan.

After testing, the infrared spectrum of the modified chitosan obtained showed a CN absorption peak of secondary amine near 1270 cm ^-1 ; a C=O absorption peak of carboxylate appeared near 1600 cm ^-1 , and an absorption peak of ketone group appeared near 1715 cm ^-1 . It can be seen that an amino acid chelate structure is indeed introduced into the structure of the modified chitosan obtained, and the weight average molecular weight of the modified chitosan is 6316, and the molecular weight distribution is 1.32.

Preparation Example 3

This preparation example is used for the modified chitosan and preparation method thereof provided by the present invention. The preparation of the modified chitosan is specifically as follows: 2,3-dibromosuccinic acid and chitosan (weight average molecular weight is 7000) are dissolved in butyl acetate according to a molar ratio of 1:0.5, and 0.12wt% of Ziegler-Natta catalyst is added. After stirring and reacting at 90°C for 6h, the reaction is filtered, washed and dried to obtain the modified chitosan.

After testing, the infrared spectrum of the modified chitosan obtained showed a CN absorption peak of secondary amine near 1270 cm ^-1 ; and a C=O absorption peak of carboxylate appeared near 1600 cm ^-1 . It can be seen that an amino acid chelate structure is indeed introduced into the structure of the modified chitosan obtained, and the weight average molecular weight of the modified chitosan is 9182, and the molecular weight distribution is 1.32.

Preparation Example 4

This preparation example is used for the modified chitosan and its preparation method provided by the present invention. The preparation method is as follows: 3-bromopropionic acid and chitosan (weight average molecular weight of 5000) are dissolved in butyl acetate in a molar ratio of 1:1, and 0.2wt% of Ziegler-Natta catalyst is added. After stirring at 90°C for 6h, the mixture is filtered, washed and dried to obtain modified chitosan.

After testing, the infrared spectrum of the modified chitosan obtained showed a CN absorption peak of secondary amine near 1270 cm ^-1 ; and a C=O absorption peak of carboxylate appeared near 1600 cm ^-1 . It can be seen that an amino acid chelate structure is indeed introduced into the structure of the modified chitosan obtained, and the weight average molecular weight of the modified chitosan is 6182, and the molecular weight distribution is 1.21.

Preparation Example 5

In this preparation example, modified chitosan was prepared according to the method provided in Preparation Example 1, except that chitosan (weight average molecular weight: 2000) was replaced by chitosan (weight average molecular weight: 7000) in an equal molar amount, and other conditions were the same.

After testing, the infrared spectrum of the modified chitosan obtained showed a CN absorption peak of secondary amine near 1270cm ^-1 ; a C=O absorption peak of carboxylate near 1600cm ^-1 ; and a C=O absorption peak of ketone group near 1715cm ^-1 . It can be seen that an amino acid chelate structure is indeed introduced into the structure of the modified chitosan obtained, and the weight average molecular weight of the modified chitosan is 9750, and the molecular weight distribution is 1.13.

Example 1

This example is used to illustrate the slow-setting water-reducing agent provided by the present invention and its preparation method. The components and contents of the slow-setting water-reducing agent are specifically: 19.5 parts by mass of the modified chitosan provided in Preparation Example 1, 0.4 parts by mass of an air entraining agent, 0.1 parts by mass of a water retaining agent and 80 parts by mass of a polycarboxylic acid.

In this embodiment, the preparation of the slow-setting water reducer specifically includes: taking the modified chitosan, air entraining agent and water retaining agent according to the above mass parts, adding them into the polycarboxylic acid and stirring them evenly to obtain the slow-setting water reducer.

Example 2

This example is used to illustrate a slow-setting water reducing agent and its preparation method. The components and contents of the slow-setting water reducing agent are specifically: 49.5 parts by weight of the modified chitosan provided in Preparation Example 1, 0.3 parts by weight of an air entraining agent, 0.2 parts by weight of a water retaining agent, and 50 parts by weight of a polycarboxylic acid.

In this embodiment, the preparation of the slow-setting water reducer specifically includes: taking the modified chitosan, air entraining agent and water retaining agent according to the above mass parts, adding them into the polycarboxylic acid and stirring them evenly to obtain the slow-setting water reducer.

Example 3

This example is used to illustrate a slow-setting water reducing agent and its preparation method. The components and contents of the slow-setting water reducing agent are specifically: 29.2 parts by mass of the modified chitosan provided in Preparation Example 3, 0.4 parts by mass of an air entraining agent, 0.4 parts by mass of a water retaining agent, and 70 parts by mass of a polycarboxylic acid.

In this embodiment, the preparation of the slow-setting water reducer specifically includes: taking the modified chitosan, air entraining agent and water retaining agent according to the above mass parts, adding them into the polycarboxylic acid and stirring them evenly to obtain the slow-setting water reducer.

Example 4

This example is used to illustrate a slow-setting water reducing agent and its preparation method. The components and contents of the slow-setting water reducing agent are specifically: 19.5 parts by mass of the modified chitosan provided in Preparation Example 4, 0.4 parts by mass of an air entraining agent, 0.1 parts by mass of a water retaining agent, and 80 parts by mass of a polycarboxylic acid.

In this embodiment, the preparation of the slow-setting water reducer specifically includes: taking the modified chitosan, air entraining agent and water retaining agent according to the above mass parts, adding them into the polycarboxylic acid and stirring them evenly to obtain the slow-setting water reducer.

Example 5

In this example, a slow-setting water-reducing agent was prepared according to the method provided in Example 1, except that the modified chitosan provided in Preparation Example 1 was replaced by the modified chitosan provided in Preparation Example 5 in equal parts by weight, and other conditions were the same.

Comparative Example 1

The comparative example provides a water reducing agent, which is prepared by uniformly mixing 40 parts by mass of PCE-S with 60 parts by mass of water.

Comparative Example 2

This comparative example is prepared according to the method provided in Example 1, except that An equal amount of Sika retarder H-1 was used to replace the modified chitosan provided in Preparation Example 1, and other conditions were the same.

Comparative Example 3

This comparative example prepares a slow-setting water-reducing agent according to the method provided in Example 1, except that the modified chitosan provided in Preparation Example 1 is replaced by an equal amount of polycarboxylic acid, and other conditions are the same.

Comparative Example 4

This comparative example is used to illustrate a slow-setting water-reducing agent and a preparation method thereof, wherein the specific components and their weight parts are: 19.5 weight parts of modified chitosan, 0.4 weight parts of air entraining agent, 0.1 weight parts of water-retaining agent and 80 weight parts of polycarboxylic acid. The preparation of the slow-setting water-reducing agent specifically comprises: taking the modified chitosan, air entraining agent and water-retaining agent according to the above weight parts, adding them to the polycarboxylic acid and stirring them evenly to obtain the slow-setting water-reducing agent.

The preparation of modified chitosan includes: taking propionic acid and chitosan (weight average molecular weight of 2000) to react according to the molar ratio of 1:0.1, firstly adding chitosan to acetic acid solution with a mass fraction of 75% for ultrasonic dispersion for 25 minutes, then adding propionic acid, stirring for reaction for 45 minutes, filtering, washing and drying to obtain modified chitosan. After testing, the obtained modified chitosan has a CN absorption peak of secondary amine near 1270cm ^-1 ; a C=O absorption peak of ketone group near 1715cm ^-1 ; and a C=O absorption peak of aldehyde group near 1740cm ^-1 . It can be seen that the structure of the obtained chitosan does not introduce amino acid chelate structure, and the weight average molecular weight of the modified chitosan is 4893, and the molecular weight distribution is 1.32.

Test Case

Concrete was prepared according to the mix ratio in Table 1, and the water reducing agents obtained in the above embodiments and comparative examples were added to the concrete at 0.5% (solid content), and the specific amount of each water reducing agent was such that the slump of the concrete was 200±10 mm. The performance indicators were then tested according to GB8076-2008 "Concrete Admixtures", and the results are shown in Table 2.

Table 1 (parts by mass)

Table 2

It can be seen from the test results that, compared with Comparative Examples 1 to 4, the modified chitosan provided by the present invention can cooperate with polycarboxylic acid to achieve better water reduction effect, slow setting effect and collapse retention effect, and has good application prospects.

Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims (10)

A modified chitosan, characterized in that the modified chitosan is a compound having an amino acid chelate-like structure bonded to the chitosan molecular chain, and the structure of the modified chitosan comprises at least one of the structural unit 1 represented by formula (1), the structural unit 2 represented by formula (2) and the structural unit 3 represented by formula (3);
In formulae (1) to (3), _R1 , _R2 , _R3 , _R4 , _R5 and _R6 are independently carbonyl, C1-C4 alkylene, C1-C4 haloalkylene, C1-C4 carboxylic acid group, C1-C4 halocarboxylic acid group, C2-C4 acyl group or C2-C4 haloacyl group. The modified chitosan according to claim 1, characterized in that in formulas (1) to _{( 3} ), _R1 , _R2 , _R3 , _R4 , _R5 and _R6 are _{independently -CH2CO- , -CH2CH2CO- ,} -CH2CH2CH2CO-, -CH2CH2-, -CH[ _CH2 (Cl)COOH]- or -CH[ _CH2 (Br)COOH] _- . The modified chitosan according to claim 1, characterized in that the chitosan is oligo-chitosan and/or high-molecular-weight chitosan; Optionally, the weight average molecular weight of the modified chitosan is 300 to 50,000, and the molecular weight distribution is 1.2 to 1.35. A method for preparing modified chitosan, characterized in that the method comprises: taking chitosan and halogenated carboxylic acid for halogenated carboxylic acid reaction under the action of a catalyst to obtain the modified chitosan. The method for preparing modified chitosan according to claim 4, characterized in that the chitosan The weight average molecular weight of polysaccharide is 300 to 50,000; Optionally, the halogenated carboxylic acid is selected from one or more of 3-chloropyruvic acid, 3-bromopyruvic acid, 2-dichlorosuccinic acid, 2,3-dichlorosuccinic acid, 3-chloropropionic acid and 3-bromopropionic acid; Optionally, the catalyst is selected from one or more of a Ziegler-Natta catalyst, a MOFs catalyst and a copper oxide catalyst; Optionally, the molar ratio of chitosan to halogenated carboxylic acid is (0.01-2):1; Optionally, based on the total molar amount of the chitosan and the halogenated carboxylic acid, the added amount of the catalyst is 0.01-0.5 wt %. The method for preparing modified chitosan according to claim 4 is characterized in that the temperature of the halogenated carboxylation reaction is 85 to 95° C. and the time is 4 to 10 hours. The modified chitosan is prepared by the preparation method according to any one of claims 4 to 6. A slow-setting water reducer, characterized in that the slow-setting water reducer comprises the modified chitosan according to any one of claims 1 to 3 and 7. The slow-setting water-reducing agent according to claim 8, characterized in that the slow-setting water-reducing agent further comprises polycarboxylic acid, an air entraining agent and a water-retaining agent; Optionally, the content of modified chitosan in the slow-setting water-reducing agent is 15 to 50 parts by mass, the content of polycarboxylic acid is 50 to 80 parts by mass, the content of air entraining agent is 0.1 to 0.5 parts by mass, and the content of water-retaining agent is 0.1 to 0.5 parts by mass. Use of the modified chitosan according to any one of claims 1 to 3 and 7 and/or the slow-setting water-reducing agent according to claim 8 or 9 in the field of construction.